Manufacture of hollow metal bars



Feb. 23, 1932. Q EN T 1,847,019

MANUFACTURE OF HOLLOW METAL BARS Filed June 25, 1930 IN VEN TOR.

A TTORNEYS.

' length, and when fracture occur, the remainlng part of the core Patented Feb. 23, 1932 UNITED TsTAT es PA ENT] eToF-FLII CE I LENNART NOBDENFELT, or norons; 'swnnnn MANUFACTURE OF HOLLOW METAL BARS} Application filed June 25, 1930, Serial no; 463,835, and in Sweden June 28,1929.

The present invention relates to a process of manufacturing hollow metal bars or tubes,-

for instance mining drills, boiler stay-bolts, from hollow billets or ingots, and, more particularly, the invention relates to an improve. ment of the process consisting therein that a core is inserted into a hole in the blank. The blank then is rolled, forged or stretched in order to receive the shape aimed at, and, to allow the core to beremoved from the finished object, said core then being exposed to a stretching operation so as to reduce its diameter.

In processes, hitherto known and based upon this principle, the last mentioned operation, viz. the stretching of the core and its removing from the object, has presented great difliculties, as the core material used, viz. common steel or forgeable iron, at the stretching operation is exposed only to local contractions, and even if the stretching process has been carried to the stress of ultimate tenacity, considerable portions of the core still present the same diameter as the inner diameter of the hole made in the blank, and offer a great resistance to the removal of the core, thus making the work more expensive. The appearance of local contractions depends on the presence of a strong friction betweenthe core and the walls of the hole.

' If this friction is not overcome a contraction evenly distributed along the whole length of the core will not take place, on the contrary the core at the stretching operation will be lengthened at the two points where a groove has been made in the ready-made blank and where no local friction thus is to be found. Thus, the stretching takes place along a very short portion of the cores the local contraction and will remain in the blank practically without any reduction of its diameter. In order to obviate this inconvenience it has been suggest-v ed to use a metal or metal alloy as core maalso be safelyremoved from the metal bar" rial must have a strength tenacity greater j than the resistance caused by friction between the coreandthe walls ofth'e hole. In such a case .the resistance, due, to friction, will positively be overcome," and the evenly distribut i ed'extenslon and thus also-thec'ontraction are 5-5 free to takeplace along the whole length of the core. Thlis,the core, after thefs'tretching operation may safely be removed from, the metalbarasawhole. Y, According to the presentinvention a proc 60 ess issuggested byJneans of which the re sistance due to friction between thelc'ore and the metal .bar at the stretching of, the "core is highlyreduced sothat' core materials, also having "low strength of ultimate tenacity ma'ybeused. a The invention'is essentially characterized by the fact that the core from the beginning is made with a diameter shorter than th'atfof the hole in the blank,'soth'at the core will not fill .it, and.further'thereby that the inter; space,"thus produced, isfilledeitherby .ap plying'a; suitable friction reducing' material roundythe" core before inserting the latter into the hold of the blank orbillet. When removing the core the lengthening properties ofthe core hereby will always be positively utilized and, 'owing thereto, the core may as a-whole. r ,7 0 Asfexamplesof'materials suitable "fto. be inserted in order to reduce the resistance, due to friction between the coreand the walls of the hole, sheets or: strips of asbestos or similar material may be employed, i

In the accompanying drawings '1 H """Figurel is'a perspective view showing a core being inserted into'the hole of thebillet'. Fig. 2 is a view, showing a'core in thefact of being wrapped with thesh'eet materiali v Fig. 3 is a View showinga core spirally Wrapped with a strip of material.

Referring to the drawings, 1 designates the billet or blank and 2 the longitudinal holes therein. As shown in Fig. l, the core 3 is wrapped with a sheet 4 of asbestos or other suitable material, the Wrapping taking place before the core is inserted in the hole 2. In Fig. 3, in lieu of a sheet of material, a strip of similar material 5 is spirally wrapped around the core before insertion into the hole 20f the:billet. ,j f

It willthusbeseen that'the-=material is wrapped in a suitable manner roundthe core. which thereupon is introduced .into the hole of the billet or blank. The rolling, forging" or stretching then taking placesoas to -allow:

rallywrappingupon a metal core, a strip of frictlon reducing material, the corebeing of a diameter less than the diameter of the hole, then inserting the core in the hole of the billet so that the Wound strip will occupy the entire'spacebetween the core and wall of the hole of the billet then elongating and reducing the cross sectional area of the billet,

and then pulling. the core and wrapping as a whole from the billet.

In testimony whereof I have affixed my signature... p

- NORDE'NEE'LT.

the blank to receive the desired shape. lAt 7 this time, .oficourse, as well .tllCOIfG inserted;

into the blank asthe friction reducing materialaregiv'enia; corresponding deformation,

section of the:friction reducinginaterial are proportionally reduced, .while: theblank is brought to the desired shapef O'Wingtotliis facta layertof the friction reducin'g'material and-,i generally, it is theimatter'ofextending will always 'positively be obtained roundthe 7' core in the blank. 'f p I g The f advantage; arrived *atby' the invention now appears at" the following operation",

namely at the removing; of. thecorr which 'acoording to the present" invention willf be removediyery'easi'ly On account f theffriction" hetween tlie core and; the walls'fof. the; hole having in'" a" Very efficient manner been reduced to. an.

order of magnitude fanbelowthe-stress of ultimate tenacity of the" core materiafithe core may very easily be removedonlyfafter a j relatiyely g inconsiderablet stretching, this stretehingfoperation positively causing; an

essentially" uniform lengtheningof the en tire length of the core soas to allow. the core diameter to: obtain a; uniform reduction; whereby the core will restlo'osely inf the ba-r atitheend ofthe stretching-operat'iori:

"Having now particularly; described the l natureofmy invention and the manner of its, operationpwhatl'"; claim-is 1; Process of'r 'making hollow; metal liars from hollow billets which consists in wrapping a metal core with a sheet offfi'iction reducingmaterial,thecorebeing ofa diamj V eterlesi'sjthanithe hole of the. billet, then insertinggth'e wrapped core intorthe hole of'tlie billet .fs'o. that the, wrapping; will occupy the entire space between the. core and'fwall ofthe billet hole, then elongating. and reducing f 7 the cross sectional T areaofitheb'illet, and then pullihgthe. coreand wrapping'ras .a whole fromtlie-billet. V x J 2,. Process .of'; making hollow ,.metal-;bars from hollow billets which consistsin spi iEO 

